|National Seasonal Rainfall Outlook: probabilities for October to December 2006, issued 26th September 2006|
Drier conditions more likely in SE & NE Australia
There is a moderate shift in the odds towards drier than normal conditions for the December quarter (October-December) in parts of southeast and northeast Australia, the Bureau of Meteorology announced today. In contrast, parts of Australia's northwest face the prospect of increased seasonal falls. Across the rest of the country, the chances are generally close to 50% for accumulating at least median rainfall during the coming three months.
The pattern of seasonal rainfall odds across Australia is a result of higher than average temperatures in both the Pacific and Indian Oceans, the former of which has been warming strongly in the past few months.
For the total over the October to December period, the chances are between 30 and 40% for above median rainfall across most of Victoria, Tasmania, southeast and southern SA, as well as over much of far northern Queensland (see map). Along parts of the south coast and Tasmania's north coast the probabilities drop below 30%. Looking at the flip-side, these probabilities mean that BELOW median falls have about a 60 to 70% chance of occurring.
So in years with ocean patterns like the current, about six or seven December quarters out of ten are expected to be drier than average in these various parts of eastern and southern Australia, with about three or four out of ten being wetter.
In contrast, a region covering part of the northwest and interior of WA has a 60 to 65% chance for the October to December rainfall total to exceed the long-term median. This equates to six seasons being wetter than average and four drier for every ten years with ocean temperatures similar to the present.
Outlook confidence is related to how consistently the Pacific and Indian Oceans affect Australian rainfall. During the December quarter, history shows this effect to be moderately consistent across much of the country (see background information).
The Southern Oscillation Index (SOI), negative for the fourth straight month, dropped from −9 in July to a low −16 in August. The approximate SOI for the 30 days ending 19th September was −4.
In addition to the low SOI, the equatorial Pacific has been warming and the Trade Winds have been weak. These ENSO indicators are all consistent with the development phase of an El Niño event, the likelihood of which has risen strongly in the past month. For routine updates and comprehensive discussion on the latest data relating to ENSO, together with details on what the phenomenon is and how it has affected Australia in the past, please see the ENSO Wrap-Up.
Click on the map above for a larger version of the map. Use the reload/refresh button to ensure the latest forecast map is displayed.
|The following climate meteorologists in the National Climate Centre can be contacted about this outlook: Grant Beard on (03) 9669 4527, Blair Trewin on (03) 9669 4623, Robert Fawcett on (03) 9669 4296.|
Regional commentary is available from the Climate and Consultancy Sections in the Bureau's Regional Offices:
THE NEXT ISSUE OF THE SEASONAL OUTLOOK IS EXPECTED BY 26th OCTOBER 2006